Tunable oscillator



April 27, 1948. B. w. HARGROVE TUNABLE OSCILLATOR Filed Sept. 20, 1944 2Sheets-Sheet 1 April 27, 1948. B. w. HARGROVE 0,

TUNABLE OSCILLATOR Filed Sept. 20, 1944 2 Sheets-Sheet 2 Patented Apr.27, 1948 UNITED STATES PATENT OFFICE (Granted under the act of March 3,1883, as

amended April 30, 1928; 370 0. G. 757) 2 Claims.

The invention described herein may be manufactored and used by or forthe Government for governmental purposes, without the payment to me ofany royalty thereon.

This invention relates to tuning arrangements and more particularly to anovel variable capacitor therefor of use with oscillators, and the like.

The objects of the present invention include the provision of a novelvariable capacitor that provides a low minimum capacity, low strayinductance and a high ratio between maximum and minimum capacity.

With the above and other objects in view, which will be apparent tothose who are familiar with capacitors and the like from the followingdescription, illustrative embodiments of the present invention are shownin the accompanying drawings wherein:

Fig. 1 is a perspective view of one embodiment of the present invention;

Fig. 2 is a perspective view of a second embodiment of the presentinvention;

Fig. 3 is a sectional View taken longitudinally of the construction thatis shown in Fig. 1;

Fig. 4 is a sectional view taken along the line 3-4 in Fig. 1; and

Fig. 5 is a perspective view of another embodiment of the presentinvention.

The present invention comprises an arrangement for varying the capacityin an LC circuit which comprises a pair of substantially aligned hollowcylindrical conductors I and 2 that have spaced ends connected thru asuitable inductor that may be a coil 3, a loop 4, or other suitableconductor bridging inductance part of the device.

A plunger member 5 is preferably disposed inwardly of and extendssubstantially longitudinally of the cylindrical conductors I and 2. Theplunger member 5 may be hollow or solid as preferred and is providedwith suitable handles 6 by which the plungers 5 are moved longitudinallyof the conductors I and 2. The member 5 bridges the space between theconductors I and 2 and is maintained in substantially coaxial relationtherewith by suitable means, such as by a spacing dielectric hollowcylinder I, rings, pins, or the like. Contacts 8 and 9 are provided forattaching connecting wires or the like, to the cylinders I and 2respectively.

In operation the condenser that is disclosed herein provides a maximumcondenser action when the opposite ends of the plunger 5 aresubstantially equi-distant from the spaced ends of the two outerconductors I and 2. The device provides a minimum or residual condenseraction when an end of the plunger 5 is substantially flush with one ofthe spaced ends of the conductors I or 2. In the present constructionthe residual condenser action is reduced to a negligible value. The coil3, or the loop 4, functions as an inductance.

An oscillator type arrangement of the present device is shown in Fig. 5of the accompanying drawings. In this arrangement an adjustable shortingbar I0 bridges a substantially parallel pair of the conductors 2 and isconnected thru an RF choke coil II to the positive terminal of a Bbattery, as shown. Choke I I keeps out of the B battery circuit anyresidual radio frequency currents which might result from a slightunbalance in the plate load circuit. Another adjustable shorting bar I2bridges the aligned pair of conductors I and is grounded thru a resistorI3 to prevent excessive grid currents. The handles 6 are non-conductingin both this arrangement and in the previously disclosed form of thedevice, and are bridged by an insulating bar I4 that is attached theretoand that maintains their positions with respect to each other. Thespaced ends of the aligned pairs of conductors I and 2 are connectedthru push-pull triodes I5 and I6. The conductor I of each condenser unitis connected to the grid of one of the triodes and the conductor 2 ofthat unit is connected to the plate of the same triode. The filaments ofthe triodes I5 and I6 are connected together and with the negativeterminal of the B battery on one side and thru a capacitor I I to groundon the opposite side of the trlode filaments. Capacitor I! is shunted bya grid leak resistor I8.

The operation of the device that is shown in Fig. 5 is analagous to thatof the form of the device that was shown in the other figures of thedrawings and of a usual oscillator but is characterized by improvedcharacteristics thereover. Each pair of conductors I and 2 constitutes alecher line, with the conductors of one line in end-to-end relation withthe conductors of the other line. Movement of conductor I varies thefeedback between the plates and grids to provide adjustment of theoscillator output, as well as a slight frequency adjustment.

It is to be understood that the forms of the device that are shown inthe accompanying drawings and described in the specification have beencited for the purposes of illustrating and describing the presentinvention and that various modifications may be substituted for the 3parts and components thereof without departing from the presentinvention as defined by the appended claims.

What I claim is: 1. A tunable, push-pull oscillator circuit com-.prising a pair of electron tubes each having at least an anode, acathode and a grid, a first lecher line; having a pair of spaced,parallel con-. ductors respectively connected to the grids of saidtubes, a second lecher line having a pain of spaced, parallel conductorsrespectively con nected to the anodes of said tubes, a shorting bar onsaid first lecher line connectegl tp said;

cathodes, a shorting bar on said second trans mission line connected tosaid cathode in series with a source of plate current, said lecher linesbeing aligned in end-to-end relation, and a movable metallic elementcapacitatively coupling each conductor of said first lecher line with analigned conductor of said second lecher line, 20

said metallic element overlapping only a portion of each line.

'4 2. An oscillator circuit as set forth in claim 1, wherein said lecherline conductors are hollow tubes, and wherein said metallic element ismovable within said tubes.

BERTHAL W. HARGROVE.

ItEFERENCES CITED The following references are of record in the Q fileof this patent:

UNITED STATES PATENTS

